Vegetable Disease Update 5-25-14

Potato

Strawberry

Tomato

Potato

Blackleg is caused by Erwinia spp. which also cause ‘soft rots’. The bacteria which lead to the aerial phase of Blackleg are soil-borne (originate from old crop debris) and spread by rainfall, overhead irrigation and wind. The aerial phase of Blackleg does not originate from decaying seed pieces. The bacterium can enter the plant through wounds created by cultivation or through stems damaged by blowing wind, sand or hail. Dense canopies, warm weather and prolonged periods of leaf wetness favor the spread of aerial Blackleg. Fortunately, the disease rarely extends below ground and only causes dieback of stems over time. Symptoms of the aerial phase of Blackleg first appear as an irregular, water-soaked ‘green’ decay on stems that turns light-brown to black over time. Hot, dry weather will cause infected areas to dry out and become brittle. Do any cultivating when plants are dry, cultivating in the presence of dew or wet plants may help to spread the bacterium around.

Strawberry

Leather rot can infect fruit at any stage. On green fruit, infected areas turn a dark-brown and develop a rough ‘leathery’ appearance. On fully mature (red) fruit little or no color change may occur on infected fruit however, fruit will have an unpleasant smell and taste. The pathogen (Phytophthora cactorum) overwinters in the soil in low-lying spots and becomes active during wet weather. Conditions that favor leather rot development also favor grey mold (Botrytis) development. However, fungicides for Grey mold control are not effective for leather rot control. Applications of a FRAC code 4 fungicide, such as Ridomil Gold SL (mefenoxam) at 1.0 pt/A 4SL or MetaStar (metalaxyl), or phosphite fungicide (FRAC code 33 fungicide), such as K-Phite, Rampart, or ProPhyt, prior to or at harvesting will help suppress leather rot. For more information on controlling leather rot and other important diseases of strawberry please see the 2014 New Jersey Commercial Vegetable Production Recommendations Guide.

Angular Leaf Spot – Bacterial leaf spot can cause spots on the leaves causing them to die. Infections can also become systemic killing the whole plant. Importantly, the calyx can become infected causing them it prematurely turn brown and reduce marketability of fruit. Fixed coppers applications will help suppress the spread as long as the weather remains dry. Discontinue copper applications in plant injury begins to occur, usually after 4 to 5 applications. Avoid overhead irrigation which will only make problem worse.

Tomato

Bacterial Spot and Speck – Tomato transplants with suspected symptoms can be treated with streptomycin (Agri-Mycin 17, Agri-Strep, 25) at 1 lb/100 gallons, or 1.25 teaspoon per gallon every 4 to 5 days prior to transplanting. Additionally, Kocide 3000 (copper hydroxide, FRAC code M1) has a greenhouse label for speck and spot control in the greenhouse. Apply ½ to 1.5 TBSP per 1000 sq ft. every 5 to 10 days. Remember, phytotoxicity is an important issue when apply copper in enclosed structures, see label for cautions, restrictions and liabilities. After transplanting, apply Actigard at 0.33 oz 50WG/A (see label for use), or fixed copper (M1) at 1 lb a.i./A plus a mancozeb (Dithane, Manzate, Penncozeb, M3) at 1.5 lb 75DF or OLF, or ManKocide (M1 + M3) at 2.5 to 5.0 lb 61WP/A on a 7 day schedule.